Technical Field
The present disclosure relates to wireless communications and more particularly to methods and systems for enabling spectrum sharing between radar and communications systems using advanced beacons and information sharing subsystem.
Background Information
In the United States, the Federal Communications Commission (FCC) defines “Spectrum” as the range of electromagnetic radio frequencies used to transmit sound, data, and video across the country. For example, spectrum carries voice between cell phones, television shows from broadcasters to a television, and online information from one computer to the next, wirelessly.
The FCC and the National Telecommunications and Information Administration (NTIA) share responsibility for managing the spectrum. NTIA manages spectrum used by the government (e.g., military, NASA) and the FCC is responsible for spectrum used by others, including individuals (e.g., garage door openers and wireless Internet connections), commercial operators (e.g., radio and television broadcasters, mobile phone providers), and public safety and health officials (e.g., police and emergency medical technicians).
Currently, frequency bands are reserved for different uses. For example, 88-108 MHz is used to broadcast FM radio. Whereas, one of the groups of frequency bands used for cell phones is 824-849 MHz and 869-894 MHz.
The FCC indicates that because there is a finite amount of spectrum and a growing demand for it, effectively managing the available spectrum is an important priority for the FCC. Further, the exponential growth of cellular wireless services has increased the large demand for spectrum resources. This cellular wireless growth has resulted in increasing pressure on government and military systems that have traditionally enjoyed unfettered and unrestricted access to spectrum.
However, some of this spectrum belonging to radar systems has been auctioned off to commercial wireless systems in some parts of the world. As a result, it has become difficult for certain radars to operate in these bands at these locations to conduct their missions. In some other parts of the world (e.g., United States), it has been projected that upwards of 1 GHz of spectrum will be needed to meet the needs of the commercial wireless systems. The U.S. Government is looking into new avenues to find spectrum to meet this need. A report from the U.S. President's Council of Advisors on Science and Technology (PCAST) suggests that sharing of the Government held spectrum is one of the ways by which the needs of the commercial wireless systems could be met. Radars are one such example of military systems that may allow sharing of their spectrum, provided, they are still the primary users of the spectrum, and wireless communications systems cause no harm to their operation.
It is believed that other governments have also been looking for new ways of utilizing spectrum to meet the needs of their government and military systems, as well as the burgeoning demand from commercial mobile operators. Spectrum sharing between various systems has been an on-going subject of discussions. One such example of spectrum sharing can be found in the use of Television (TV) Band White Spaces (54-88 MHz, 176 MHz-216 MHz and 470 MHz to 862 MHz) where communications systems can use the un-used channels by the TV broadcast services as long as they obey certain regulations, so as not to cause harmful interference to the TV broadcast receivers. The TV Band White Spaces regulations includes the use of a database service, that the communications devices must access, and provide their location, transmit power, antenna height and other information. Based on the operation of protected devices in that area and the protection contours that have been determined, the database services computes the available channels for the White Space (Communications) Devices (WSDs) and conveys this information using internet services to the WSDs. The WSDs can then operate on these available channels. Another example of commercial communications systems sharing the spectrum with radars can be found in the 5.8 GHz band. In this case, the communications devices (e. g. IEEE 802.11 Wi-Fi®) need to sense for radar signals. The typical characteristics of the radar signals have been provided to the commercial wireless community. If the commercial wireless devices detect the presence of these radar signals, they need to vacate the channel based on some known Dynamic Frequency Selection (DFS) algorithm. However there are known issues with DFS. If a device is misconfigured, it will not implement DFS correctly, and may cause interference to radars. Typically there is no “positive control” of the WiFi devices is possible. In addition, DFS is not very flexible. There is one “policy” which is that if a radar is sensed, the wireless systems must vacate the channel. There is no way to vary the sharing policy based on current situation, or type of wireless device, etc.
In the two examples provided, either the primary users of the spectrum are known to occupy the same channel for long time durations (e. g. TV Band Broadcasting equipment) in which case, database enabled spectrum sharing was feasible, or, it was possible to provide the radar (e. g. Weather Radar in 5.8 GHz Band) signatures to the commercial wireless devices which would then only sense for those signals.
In some cases however, radar operation and signatures cannot be easily shared with the commercial entities. This could be, when the radars are used for government and military use. In such cases, the detailed radar operation as well as signatures bear classification grade which prohibits their dissemination to commercial entities, leave alone entities that may exist in other countries. In addition, radar has a highly directional beam pattern that can change its orientation spatially on milliseconds (ms) timescales, as well as the radar pulses can hop in the frequency domain. So while in TV band, it is possible for spectrum to be shared using databases since the TV broadcast equipment does not change the frequency of its operation, it is difficult to have a database enabled spectrum sharing with radars that are used to hop over the entire available frequency band, without constraining the radar operation and hence reducing its performance.
Spectrum sensing is possible for co-existence, where communications devices sense for radar pulses, and if detected, choose to follow the guidelines as defined by the local regulations (e.g.: ceasing operation on that channel). However, that is not optimal use of the spectrum.